Hydraulic lifter assemblies for actuating intake and exhaust valves in internal combustion engines are well known. A typical lifter assembly includes a lifter body supportive of cam follower such as a roller. In use, the body is disposed for reciprocal motion in a bore in an engine block for translating rotary motion of a cam lobe into reciprocal motion of a pushrod. A piston within a well in the lifter body defines a high-pressure chamber in the well between the piston and the bottom of the well. The piston includes a low-pressure reservoir supplied with engine oil, from which the high-pressure chamber is replenished via a check valve. A pushrod seat closes the low-pressure chamber and receives the pushrod. A spring within the high-pressure chamber urges the piston outwards, thus removing mechanical lash in the valve train. The low-pressure chamber is provided with oil via an axial passage in the pushrod in communication with an oil gallery in the engine rocker arm assembly, such that there are no air voids in the oil supply system during engine operation.
It is necessary to completely purge air from an engine oil supply system after assembly of the engine and before the first starting. Of necessity, when the rocker arm assembly is bolted to the engine head, some of the intake and exhaust valves are placed in an open position. In a relatively short time, those lifter assemblies associated with the open valves will leak oil from their high-pressure chambers in response to force exerted by the valve springs. When this happens during normal operation of an engine, as during periods of inoperation, it is of little consequence, as the lifter automatically refills from the low-pressure reservoir through the check valve as soon as the engine is re-started and the force is relieved from the lifter. However, upon first starting an engine after assembly, it is essential that the low-pressure reservoir have sufficient oil to refill the high-pressure chamber immediately. A failure to provide oil for filling of the high-pressure chamber immediately results in a noisy lifter, a false indication of lifter failure, a failure of the first-start-after-assembly engine test, and substantial engine rework costs.
To guard against this problem in the prior art, lifters are carefully filled with oil after assembly of the lifter and are shipped in a vertical position. However, engine assembly can require a lifter to be placed in an orientation wherein oil can drain from the lifter. In addition, some engines have normal lifter positions wherein oil can drain from the low-pressure reservoir during and after engine assembly.
Prior to starting a newly-assembled engine, oil is forced through the oil distribution system under pressure for a predetermined time period, typically on the order of one minute, to purge air from the system. A large amount of air is initially present in galleries in the rocker arm shaft, rocker arms, and pushrods, which air must be expelled from the pushrods at or through the hydraulic valve lifters. Because there is no lash between elements in the valve-open valve trains, air purging is difficult and frequently incomplete, resulting in a noisy lifter upon initial starting. Further, any lifter with residual air trapped in the low-pressure reservoir may suck that air into the high-pressure chamber upon start-up, producing a void therein resulting in prolonged lifter noise and test failure.
What is needed in the art of hydraulic valve lifters is a means to assure purging of air from all engine pushrods and lifters prior to first starting of an engine.
It is a principal object of the present invention to prevent lifter test failure of a newly-assembled internal combustion engine.